1. Field of the Invention
The present invention relates to a magnetic head having an MIG (metal-in-gap) structure in which a metal magnetic film is formed in a gap-opposing part of a ferrite-made core, specifically to a magnetic head which is effective when the metal magnetic film described above is formed of a soft magnetic material having excellent magnetic characteristics as compared with those of conventional ones.
2. Description of the Related Art
FIG. 11 is a perspective drawing of a magnetic head, and FIG. 12 is an enlarged plane drawing obtained by seeing the magnetic head from a surface side thereof rubbed against a recording medium.
The code 1 shown in the drawings is a core formed of single-crystal ferrite comprising Fe.sub.2 O.sub.3, MnO and ZnO or a connected material of single-crystal ferrite and poly-crystal ferrite, and opposing planes 1a, 1a and inclining planes (track width-controlling planes) 1b, 1b inclining toward the opposing planes 1a, 1a described above are formed on the cores 1, 1.
Metal magnetic films 2 having a high saturation magnetic flux density such as Fe--Ta--N alloy and Fe--Al--Si alloy (sendust) are coated and formed on the opposing planes 1a, 1a and the inclining planes (track width-controlling planes) 1b, 1b described above, and the metal magnetic films 2 are connected with each other via a non-magnetic material to allow the connected part to become a magnetic gap G. Incidentally, Tw is a track width.
The code 3 is adhesive glass for connecting the metal magnetic films 2, 2 coated and formed on the opposing planes 1a, 1a, and also in the inclining planes (track width-controlling planes) 1b, 1b, the adhesive glass 3 described above is filled on the metal magnetic film 2 coated and formed on the core. The code 4 is a coil for recording or reproducing. In FIG. 12, an azimuthal angle of the magnetic gap G is zero degree but actually in the magnetic head, the magnetic gap G has an azimuthal angle in a clockwise direction or a counterclockwise direction against a magnetic circuit direction.
The magnetic head shown in FIG. 11 is formed in a .beta. azimuth in which the gap-opposing plane is formed of a (100) plane in a crystallographic plane and the tape-rubbing plane is formed of a (110) plane. The direction of the crystallographic axis along the magnetic circuit direction is a &lt;100&gt; direction.
FIG. 3 is a ternary diagram showing the composition ratio of a ferrite material comprising Fe.sub.2 O.sub.3, MnO and ZnO. The composition ratio of a ferrite material used usually in conventional magnetic heads is shown in (a) of the diagram, and the ratio Fe.sub.2 O.sub.3 :MnO:ZnO is 53 to 55 mol %:26 to 31 mol %:16 to 19 mol %.
A mol % of ZnO out of the three compounds constituting ferrite exerts a strong influence on the determination of a magnetic striction of a crystallographic axis and a mean coefficient .alpha. ferrite of thermal expansion of a ferrite material. If ZnO falls in a range of from 16 mol % to 19 mol %, both of the absolute value of a magnetic striction .lambda. &lt;100&gt; in a &lt;100&gt; direction and a magnetic striction .lambda. &lt;111&gt; in a &lt;111&gt; direction become values close to zero, and the mean coefficient a ferrite of thermal expansion of ferrite becomes about 115 (10.sup.-7 /.degree. C.) at temperatures ranging from 100 to 300.degree. C.
One reason why ZnO was changed from 16 mol % to 19 mol % in the past was that the absolute value of a magnetic striction .lambda. &lt;100&gt; in a &lt;100&gt; direction and a magnetic striction .lambda. &lt;111&gt; in a &lt;111&gt; direction could be lowered, and another one was that the mean coefficient .alpha. ferrite of thermal expansion of ferrite was made almost the same as the mean coefficient of thermal expansion of a soft magnetic material such as sendust for forming the metal magnetic film 2. A decrease in a difference between the mean coefficient .alpha. ferrite of thermal expansion of ferrite and the mean coefficient of thermal expansion of the soft magnetic material described above results in a reduction in the absolute value of a stress .alpha. total exerted in the magnetic circuit direction (&lt;100&gt; direction) of the cores 1, 1 in the vicinity of the gap G.
On the other hand, a mol % of Fe.sub.2 O.sub.3 contained in ferrite exerts a strong influence on the magnetocrystalline anisotropic energy K1 and the saturation magnetostriction .lambda.s as the whole ferrite material. If Fe.sub.2 O.sub.3 falls in a range of 53 mol % to 55 mol %, both of the absolute value of the magnetocrystalline anisotropic energy K1 and the absolute value of the saturation magnetostriction .lambda.s are reduced.
The magnetic anisotropy of a crystal axis depends only on the magnetocrystalline anisotropic energy K1 if ferrite is used alone. However, in the magnetic head shown in FIG. 11, processing strain and a difference in a coefficient of thermal expansion between the soft magnetic material constituting the metal magnetic film 2 and ferrite increase the stress .alpha. total exerted in the magnetic circuit direction (&lt;100&gt; direction) of the cores 1, 1 in the vicinity of the gap G. Thus, a magnetoelastic energy which is proportional to the product of the stress .sigma. total and the saturation magnetostriction .lambda.S each described above comes to exert an influence on the magnetic anisotropy. Accordingly, it is estimated that the magnetic anisotropy of the magnetic axis &lt;100&gt; in the magnetic circuit direction in the magnetic head shown in FIG. 11 is determined by an apparent magnetic anisotropic energy obtained by subtracting the magnetoelastic energy from the magnetocrystalline anisotropic energy K1.
That is, the apparent magnetic anisotropic energy (Ea)=(the magnetocrystalline anisotropic energy K1)-(the magnetoelastic energy 3/2.multidot..sigma. total.multidot..lambda.S) (.sigma. total: stress, .lambda.S: saturation magnetostriction)
If this apparent magnetic anisotropic energy Ea is larger than zero (Ea&gt;0), the crystal axis &lt;100&gt; becomes an easy axis of magnetization, and if it is smaller than zero (Ea&lt;0), the crystal axis &lt;100&gt; becomes a hard axis of magnetization. The more the absolute value of Ea is close to zero, the more the magnetic anisotropy is weakened.
In a conventional magnetic head, the absolute value of the magnetocrystalline anisotropic energy K1 and the absolute values of the directional magnetostriction .lambda.&lt;100&gt; and .lambda.&lt;111&gt; have been lowered respectively and the absolute value of the saturation magnetostriction .lambda.s has been reduced by decreasing the absolute value of the apparent magnetic anisotropic energy described above as much as possible, that is, making it isotropic so that the magnetic permeability having an inversely proportional relation to the apparent magnetic anisotropic energy described above can be enhanced. Further, the absolute value of the stress .sigma. total has been lowered as well by making the mean coefficient .alpha. ferrite of thermal expansion of ferrite almost the same as the mean coefficient of thermal expansion of the soft magnetic material such as sendust.
However, soft magnetic materials such as Fe--Ta--N alloy and Fe--Al--Si alloy (sendust) which have so far been used for the metal magnetic film 2 are inferior in magnetic characteristics. The Fe--Ta--N alloy is susceptible to corrosion and therefore is not excellent in a corrosion resistance. Meanwhile, the Fe--Al--Si alloy (sendust) has a low saturation flux density and therefore is likely to bring about a reduction in the head output.
Accordingly, the present inventors prepared a magnetic head in which the material described in Japanese Unexamined Patent Publication No. 7-85411 (U.S. Pat. No. 5,585,984) as a soft magnetic material having more excellent magnetic characteristics than those of conventional soft magnetic materials, that is, an iron base fine crystalline material containing crystal of carbide or nitride was used for the metal magnetic film 2 and the core 1 was formed of ferrite having the conventional composition described above to confirm the head output. The iron base fine crystalline film described above has a high saturation flux density and a high magnetic permeability, and therefore high output is expected to be obtained in itself in magnetic recording and reproducing. However, it was confirmed that the head output was reduced when magnetic recording and reproducing were actually carried out at as high frequency as several MHz to several 10 MHz.
This is estimated to originate in the fact that since the iron base fine crystalline material described in Japanese Unexamined Patent Publication No. 7-85411 (U.S. Pat. No. 5,585,984) has a higher coefficient of thermal expansion as compared with those of conventional metal magnetic films, a difference between the mean coefficient .alpha. ferrite of thermal expansion of ferrite and the coefficient of thermal expansion of the soft magnetic material (iron base fine crystalline material) described above is expanded. That is, this is estimated to be caused by the fact that the stress .alpha. total exerted in the magnetic circuit direction (&lt;100&gt; direction) of the cores 1, 1 in the vicinity of the gap G is increased and as a result thereof, the absolute value of the apparent magnetic anisotropic energy Ea is elevated, which in turn results in a reduction in the magnetic permeability having an inversely proportional relation to the apparent magnetic anisotropic energy Ea described above.